@sddfssw Just in case you don't already know, there are three versions of Sims 4: the global version (all languages), an English-only version, and a version limited to Polish, Russian, and Czech. What you want is the global version, and an EA App support rep should be able to help you get it if you don't already have it.
The EA App's inability to switch languages without reinstalling the game is a known issue that has been brought up many times. The EA people who deal with EA App issues have given no indication that this feature will be reintroduced. And from what I've seen, the App team is still putting out larger fires, so it might be a while before they move on to optional features, even the popular ones.
If your computer has the extra space for it, one potential workaround here would be to have two copies of Sims 4 installed. If you rename the "The Sims 4" folder that holds the game's program files, the EA App won't recognize the game is installed, giving you a chance to reinstall it in the other language. Then when you wanted to switch back to the first language, you'd rename the second "The Sims 4" folder and revert the first one. I haven't actually tried this, so I can't promise it'll work, but it's worth testing.
When renaming a folder, make sure the EA App is closed and the EABackgroundService is NOT running in the Task Manager. Either one can block changes to the game's program files, including renaming.